1. Field of the Invention
The present general inventive concept relates to an inkjet printhead, and more particularly, to a thermal inkjet printhead having a heater with enhanced durability protection from pressure induced by bubble extermination.
2. Description of the Related Art
In general, an inkjet printhead is an apparatus that ejects ink droplets on a desired area of recording paper in order to print predetermined color images. The inkjet printhead is categorized into two types based on the ink droplet ejection mechanism used. The first type of inkjet printhead is a thermal inkjet printhead that ejects ink droplets due to an expansion force of bubbles generated by thermal energy. The second type of inkjet printhead is a piezoelectric inkjet printhead that ejects ink droplets by applying a pressure to the ink caused by the deformation of a piezoelectric body.
The ink droplet ejection mechanism of the thermal inkjet printhead is as follows. When a current flows through a heater made of a heating resistor, the heater heats up and ink near the heater in an ink chamber, is instantaneously heated up to about 300° C. Accordingly, bubbles are generated by ink evaporation, and the generated bubbles are expanded to exert a pressure on the ink filled in the ink chamber. As a result, an ink droplet is ejected through a nozzle out of the ink chamber.
Regarding the relationship between the direction of growing an ink bubble and the direction of ejecting an ink droplet, the thermal inkjet printhead is classified into a top-shooting type, a side-shooting type, and a back-shooting type. In the top-shooting type, the growing direction of an ink bubble and the ejecting direction of an ink droplet are the same. In the side-shooting type, the growing direction of an ink bubble is perpendicular to the ejecting direction of an ink droplet. In the back-shooting type, the growing direction of an ink bubble is opposite to the ejecting direction of an ink droplet.
FIG. 1 is a schematic cross-sectional view of a conventional thermal inkjet printhead. Referring to FIG. 1, the conventional inkjet printhead has a substrate 11 on which a plurality of material layers are stacked. A chamber layer 20 is stacked on the substrate 11 and the plurality of material layers, and a nozzle plate 30 is stacked on the chamber layer 20, which defines the ink chamber 22. Ink is filled in the ink chamber 22 and a heater 13 heating the ink to generate bubbles is installed under the ink chamber 22. In addition, the nozzle plate 30 has a nozzle, which is used to eject the ink.
Also included in FIG. 1 is an insulation layer 12 formed on the substrate 11 for heat and electric insulation between the heater 13 and the substrate 11. The heater 13 used to heat the ink in the ink chamber 22 to generate bubbles is disposed on the insulation layer 12. The heater 13 is formed by depositing a thin film on the insulation layer 12, for example, tantalum nitride (TaN) or tantalum-aluminum alloy (TaAl). Conductors 14 supplying an electric current to the heater 13 are disposed on the heater 13. The conductors 14 may be made of a metal having high electric conductivity, such as aluminum (Al).
A passivation layer 15 is formed on the heater 13 and the conductors 14 to protect them. The passivation layer 15 prevents the heater 13 and the conductors 14 from oxidizing or directly contacting the ink, and is formed by depositing a protective film, for example, a silicon nitride (SiNx) film. An anti-cavitation layer 16 is formed on the passivation layer 15 to protect the heater 13 from cavitation pressure induced by bubble extermination, and is made of mainly a protective material, such as tantalum (Ta).
However, in the above-described thermal inkjet printhead, when a bubble dissipates, the induced cavitation pressure is concentrated at a certain point of the upper surface of the anti-cavitation layer 16 formed on the heater 13. The pressure may cause damage to the anti-cavitation layer 16 and the surface of the heater 13 because of a weak pressure resistance of the passivation layer 15 used to protect the heater 13. Such damage to the heater 13 decreases the lifetime of the inkjet printhead.